<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>1</button>
    <button>2</button>
    <button>3</button>
    <button>4</button>
    <button>5</button>
</body>
</html>
<script>
    var a=document.querySelectorAll("button")
    for(var i=0;i<a.length;i++){
        a[i].onclick=function(){
            for(var i=0;i<a.length;i++){
                a[i].style.backgroundColor=''
            }
            this.style.backgroundColor='yellow'
        }
    }
</script>